(a) Field of the Invention
The present invention relates to improvements in the plates used in a condenser.
(b) Description of the Prior Art
Generally, it is film coefficient that becomes a problem in improving the ability of the plate type condenser to transfer heat for condensation. Film coefficient is an index of easiness of heat transfer on the heat transfer surface and is defined as (the thermal conductivity of the film)/(the film thickness) and it varies with the condition in which the condensate adheres to the heat transfer surface. If vapor is fed to a vapor chamber, condensate like a thin film will form on all the heat transfer surface. As the condensation continues, the film becomes progressively thicker until it flows down along the heat transfer surface under its own weight while forming a thick filmy downflow liquid layer on the heat transfer surface in the middle lower area over the substantially entire width thereof, said downflow liquid layer being progressively thicker, as the bottom is approached. The heat transfer surface thus covered with the downflow liquid is prevented from contacting the vapor and the thick film of liquid greatly decreases the film coefficient and hence lowers the heat transfer performance. Therefore, in order to improve the heat transfer performance of the entire heat transfer surface on which vapor condenses, some means will be required which minimize the area of the filmy downflow liquid layer and which prevents said film from growing too thick.
The applicant has previously proposed a condenser (Japanese Patent Application No. 152364/75) which comprises a condensate collecting and discharging mechanism (water collecting means) provided in each fixed region of a condensing and heat transfer surface, and longitudinal grooves disposed between such water collecting means and extending in the direction of flow of condensate. An outline of this arrangement is as follows.
As shown in FIGS. 1 and 2, a plate 1 is provided with water collecting means each comprising a hill-like inclined groove 2 and vertical grooves 3 and opening to a vapor passage side A, and a group of longitudinal grooves 4 extending in the direction of flow of condensate are formed between adjacent water collecting means 2, 3 to open at their lower ends to said inclined groove 2. The function and effect of the water collecting means are such that the condensate which forms on the heat transfer surface is drawn to the valleys 4a of the longitudinal grooves 4 by the action of surface tension to form downflow liquid layers only in the valleys 4a, and the condensate thus collected in the valleys 4a flows down under its own weight and is collected and discharged by the water collecting means 2, 3. As a result, the downflow liquid layers are considerably reduced when considered from the entire heat transfer surface, so that the heat transfer performance is improved.
However, since the direction in which the vapor is fed extends from the top and opposite lateral sides of the plate 1 and since, on the other hand, the inclined grooves 2 of the water collecting means 2, 3 provided on the plate 1 are inclined like a hill, as described above, there are many places where the direction of flow of the condensate is opposed to the direction of flow of the vapor when the condensate is moved downward while moving slantwise along the inclined grooves 2. At said places, the condensate will flow counter to the flow of the vapor. Therefore, the condensate is pushed back by the vapor stagnant in the inclined grooves 2 and meets the succeeding condensate, with the inclined grooves 2 becoming locally clogged, so that the condensate floods the inclined grooves 2 to flow down to the lower heat transfer surface region. As a result, the film on the heat transfer surface becomes thick again and grows broader, decreasing the film coefficient and lowering the heat transfer performance.